But thats the thing…no one thinks its a guy running around in a costume…they think its some sort of creature

This would be accurate following his first appearances, but most would eventually realize he is not some sort of creature.......especially if he drives "the" muscle car of Gotham City. However that realization would not diminish the fear factor one bit, which is why he embraces the image of the bat as his signature.
And let's not forget his detective skills and intellect which contribute to the fear he instills. Surely his ability to stay many steps ahead of his prey and to always be in the right place at the right time must weigh heavy on Gotham's underworld.

Re. the trunks......for both Batman and Superman.......I just think the aesthetic of the costume is better with them......with no rhyme or reason for their presence other than that. There are many super-heroes created at the same period as Batman and Superman whose costumes do not include trunks, so the idea that trunks are "dated" seems mis-informed to me. If they are "dated" why don't all the heroes created around the same date also sport trunks.......For me the answer is more likely that the aesthetic of the individual design did not require trunks?